Lens useful as a keratoscope

ABSTRACT

A toroidal lens (10) or a plurality of such lenses attached to a handle (14) for use as or in a keratoscope (12). If a plurality of lenses are employed, they are arranged either in different planes parallel to each other or concentrically in a single plane with varying degrees of ellipticity.

DESCRIPTION

The present invention relates to a lens useful as a keratoscope.

BACKGROUND OF THE INVENTION

There are situations in which it is necessary to obtain an assessment ofthe degree of astigmatism of a cornea of an eye. For example, when asurgeon has made an incision in the cornea as part of an operatingprocedure such as insertion of an intraocular lens, it is necessary atthe end of the procedure to close the incision by means of sutures.However, the sutures have to have an appropriate degree of tension toavoid inducing excessive stigmatism in the cornea. The lens of thepresent invention enables the surgeon to monitor readily the degree ofastigmatism in a cornea as suturing is in progress and to adjust thetension of the sutures if necessary.

For example, closure of the surgical wound following cataract extractionand intraocular lens implantation may result in significantpostoperative astigmatism. The amount of astigmatism is oftenunpredictable and may be a major factor limiting visual recovery and thefinal result of the procedure.

As surgical techniques and lens design have improved, other more seriouscomplications have reduced in frequency. Patients' expectations havealso increased and an excellent visual result following surgery isconsidered one in which patients not only have good corrected acuity,but are also able to see well without spectacles. The major problemwhich prevents ophthalmic surgeons from obtaining such a result is oftenthe presence of surgically induced astigmatism. The introduction ofmultifocal and bifocal implants is another factor suggesting that levelsof astigmatism previously considered routine may no longer beacceptable. At a recent conference (EIIC 1988) in Copenhagen, a panel ofexperts uniformly agreed that surgically induced astigmatism was themajor remaining problem with their surgery over which they hadinadequate control. This is one of the reasons why phacoemulsificationand small incision cataract surgery is being considered by an increasingnumber of surgeons.

Even with these advanced techniques, astigmatism can still be a problemif wound closure and suture tension is not carefully monitored. SurgicalKeratometers have been introduced to enable surgeons to monitor thecorneal astigmatism during wound closure and adjust suture tensionaccordingly. These instruments have varied from complex and expensiveinstruments such as the Terry Keratometer to simple metal or plasticdevices such as the Karickoff device which reflect a circle of light onthe cornea. All these devices operate in a similar principle in that thereflected image of a circular light source will have an elliptical shapeif significant astigmatism is present. More expensive instruments useincandescent or fibreoptic light sources to provide a bright imagewhilst the cheaper qualitative keratometers use reflected light from ametal or plastic circle. Unfortunately, the brightness of the cornealimage with the qualitative keratometers is inadequate and the reflectionis difficult to recognise. These qualitative keratoscopes have to beheld at just the right angle to produce an image which is oftendifficult to recognise. The more expensive Keratometers produce adequateimages, but are complex and time consuming. This has restricted theiruse to a small number of surgeons. The lens of the present invention isrelatively inexpensive to produce compared to known qualitativeKeratoscopes whilst providing a relatively bright reflected cornealimage compared to known qualitative Keratoscopes.

SUMMARY OF THE INVENTION

In accordance with one aspect of the present invention, there isprovided a lens useful as a keratoscope which is a light transmittinglens of annular shape with a toroidal surface.

Preferably, the annular light transmitting lens is of circular orsemi-circular profile in cross-section.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described, by way of example, withreference to the accompanying drawings, in which:

FIG. 1 is a sectional view of a toroidal lens of circular cross-sectionuseful as a keratoscope in accordance with the present invention;

FIG. 1a is a sectional view of a toroidal lens of semi-circularcross-section useful as a keratoscope in accordance with the presentinvention;

FIG. 2 is a perspective view of the toroidal lens of FIG. 1;

FIG. 3 is a plan view of a hand-held keratoscope using the lens of FIGS.1 and 2;

FIG. 4 is a plan view of a hand-held keratoscope including a pluralityof the lenses of FIGS. 1 and 2 with all of the lenses being in a singleplane;

FIG. 5 is a plan view of a keratoscope similar to FIG. 4 except thatmiddle and outer lenses are of elliptical shape;

FIGS. 6 to 8 show reflected images obtained from surfaces havingdifferent degrees of asymmetry using the keratoscope of FIG. 5;

FIG. 9 is a perspective view of a keratoscope having a plurality oflenses similar to that shown in FIG. 4, except that the lenses are indifferent planes;

FIG. 10 is a sectional view through the keratoscope of FIG. 9 to showthe cross-sectional profile and disposition of the lens;

FIG. 11 is a schematic view of a beam splitter and reflector arrangementfor use with the lens of the present invention;

FIG. 12 is a schematic view of a beam splitter and multiple reflectorarrangement for use with the lens of the present invention;

FIGS. 13 and 14 are views of the respective containers for intraocularlens having a keratoscope according to FIG. 3 releasably attachedthereto;

FIG. 14a is a plan view of a chart which can be used in conjunction withthe lens of the present invention.

FIG. 15 is a plan view of a hand-held keratoscope incorporating a numberof lenses in accordance with the present invention mounted on arotatable member in a circle about the periphery thereof; and

FIG. 16 is a schematic view of a binocular microscope incorporating areticule in an eye piece for use in conjunction with the lens of thepresent invention.

DESCRIPTION OF THE INVENTION

In FIGS. 1 and 2, there is shown a toroidal lens 10 useful as akeratoscope which is of a shape formed by rotating a circle about a linein its plane but not intersecting it. Thus, the toroidal lens iscircular in cross-section as shown in FIG. 1, but forms a closed ring orannulus as shown in FIG. 2.

The lens 10 is formed of light transmitting material such as plasticsmaterial or glass.

Whilst the toroidal lens of FIGS. 1 and 2 has a body of circular profilein cross-section, it is envisaged that the body of the lens 10 couldhave other profiles. For example, the lens 10 could be of semi-circularprofile in cross-section as shown in FIG. 1a.

The lens 10 can be used as a keratoscope by placing the lens between asource of light and an eye of a subject. The lens 10 produces a focusedcircular light image which is reflected from the corneal surface of theeye. If the cornea is completely spherical, then the reflected imagewill be circular. However, if the cornea is not completely spherical andshows significant astigmatism, the reflected image will have anelliptical shape.

Conveniently, as shown in FIG. 3, the lens 10 may be incorporated in akeratoscope 12 having a handle 11 attached to the lens 10 to enable thelens 10 to be manually manipulated and moved relative to the eye beingobserved. The position of the lens 10 relative to the cornea is notcritical for obtaining a reflected image. An image will be obtained in alarge range of distances from the corneal surface. However, the size ofthe reflected image will vary with the distance of the lens from thecorneal surface.

Conveniently, the lens 10 is used in conjunction with a microscope whichalso provides a source of light to enable an operator to view thereflected image in the eye piece of the microscope. In this connection,the lens 10 is placed between the objective lens and the eye and focusesthe co-axial light from the microscope.

In FIG. 4, there is shown a keratoscope 12 comprising a handle 14 andthree concentric circular toroidal lenses 10 of progressively increasingsize disposed in a single plane. The lenses 10 are of the same generaltype as the lens of FIGS. 1 and 2.

The multiple toroidal lenses of the keratoscope 12 can be used toprovide multiple nested images which are reflected from the cornealsurface. Conveniently, the three rings of the keratoscope can bedifferently coloured for easier interpretation of the results obtained.

In FIG. 5, there is shown a keratoscope 16 comprising a handle 18 andthree nested annular toroidal lenses 10a, 10b, 10c which are ofprogressively increasing size, respectively. The innermost lens 10a iscircular, the intermediate lens 10b is slightly elliptical and the outerlens 10c is substantially elliptical. Whilst three lenses ofprogressively increasing ellipticity with increasing size have beenshown, it is envisaged that more lenses of ever increasing size andellipticity could be added to the apparatus of FIG. 5.

If the cornea is completely spherical, then the reflected image of thering 10a will be circular. However, if the cornea is not completelyspherical and shows significant astigmatism, the reflected image of thering 10a will not appear circular, but will have an ellipticalconfiguration. If the long axis of the elliptical rings of thekeratoscope 16 are aligned with the short axis of the reflectedelliptical image of the inner ring from the corneal surface, then anoperator can obtain an estimation of the degree of astigmatism of thecornea. This orientation can be achieved simply by rotating thekeratoscope 16 by means of the handle 18.

If the degree of astigmatism in the cornea being investigated ismoderate, then the second reflected ring image from the lens 10b willappear circular.

Further, if the degree of astigmatism in the cornea being investigatedis large, then the outer ring will appear closest to a circle. Byvarying the degree of ellipticity of the plurality of toroidal lens, itis possible to calibrate the degree of astigmatism.

For example, in the reflected image of FIG. 6, the inner ring iscompletely circular which represents an image reflected from the lens10a, is completely circular. This indicates a spherical cornea withlittle or no astigmatism. In FIG. 7, the middle ring is completelycircular whilst the inner and outer rings are elliptical. This indicatesan eye with a moderate degree of astigmatism of about 3 diopters. As canbe seen in FIG. 7, the long axis of the ellipse of the inner ring isdisposed at 90° to the long axis of the ellipse of the outer ring.

In FIG. 8, the outer ring is completely circular whilst the inner andmiddle rings are elliptical. This indicates an eye with a large degreeof astigmatism of about 6 diopters. As can be seen in FIG. 8, the longaxes of the ellipses of the inner and middle rings are disposed at 90°to the long axes of the ellipses of the middle and outer rings of FIG.6.

The ellipticity of the outer rings could be changed from that shown inthe drawings depending on the sensitivity of the keratoscope and therange of astigmatism desired to be measured.

In FIG. 9 there is shown a variation in the keratoscope 12 of FIG. 4.The keratoscope 20 shown in FIG. 9 has a plurality of concentric lenses22 which are disposed in different planes, and a handle 24. As can bestbe seen in the transverse cross-section of FIG. 9 shown in FIG. 10, thelenses 22 are of progressively increasing size, but are located indifferent planes. In this way, the reflected images are of varying sizedepending on the distance of the lenses 22 from the eye. The lens 22which is further from the eye has a correspondingly smaller imagecompared to lenses 22 which are closer to the eye.

The distance between the reflected rings mat therefor be adjusted byhaving the lenses in different planes. For example, a plurality oflenses in the same plane will produce reflected rings which may not beequidistant since the cornea is a curved reflecting surface. However, aplurality of lenses in different planes on an arc or curvaturecorresponding to that of the cornea will produce equidistant reflectedrings. Alternatively, in some circumstances, it may be desired to invertthe keratoscope of FIGS. 9 and 10 and have the smaller ring closest tothe eye.

The construction shown in FIGS. 9 and 10 may conveniently be obtained bymoulding a single piece of plastics material.

In FIG. 11, there is shown an apparatus which provides a combination ofa keratoscope ring produced using an apparatus in accordance with thepresent invention and a simultaneous circular image for comparisonpurposes. The apparatus of FIG. 11 comprises a beam splitter 30 and aconvex or concave mirror or other reflective surface 32. The surface 32has a radius of curvature which is the same as that of a cornea 34 whenin a non-astigmatic state.

In use, the beam splitter 30 reflects some of the ring of incident lightfrom a lens of the present invention through 90° to the surface 32. Thesurface 32 reflects this ring of light back to the beam splitter 30.Some of this ring of light reflected from the surface 32 whichcorresponds with a circular image 36 obtained from a non-astigmaticcornea is reflected back towards an eye of the operator. Simultaneously,some of the ring of incident light travels straight through the cornea34 and is reflected straight back through the beam splitter 30. If thecornea 34 is astigmatic, a reflected keratoscopic image 38 from thecornea 34 will be elliptical as shown in FIG. 11. The elliptical image38 reflecting from the cornea 34 and the circular image 36 reflectedfrom the surface 32 are superimposed at the eye of the observer so thatthe observer can obtain an immediate comparison of the two reflectedimages 36 and 38 and thus assess the degree of astigmatism of the cornea34. The use of a curved surface 32 enables the image 36 reflectedtherefrom to be of similar size to the keratoscope image 38 reflectedfrom the cornea which assists in the comparison referred to. A colourfilter 40 may be interposed between the beam splitter 30 and the surface32 so that the reflected circular image 36 is differently coloured fromthe keratoscopic image 38 reflected from the cornea 34 to aid in thecomparison.

Further, the surface 32 may be moveable away from and towards the beamsplitter 30 and be mounted for this purpose on a calibrated micrometer(not shown). This enables the surface 32 to be moved in a calibratedmanner relative to the beam splitter 30. The size of the reflectedcircular image 36 varies according to the distance of the surface 32from the beam splitter 30. Thus, where the keratoscopic image 38 iselliptical the surface 32 can be moved to a position at which thecircular image 36 has a diameter corresponding with the length of thelong axis of the ellipse of the image 38. The callibration enables theoperator to obtain an accurate measurement of the degree of ellipticityof the keratoscopic image 38 and thus the degree of astigmatism of thecornea 34.

In FIG. 12, there is shown an apparatus which provides a combination ofa keratoscopic image produced using an apparatus in accordance with thepresent invention and a plurality of simultaneous circular images forcomparison purposes. The apparatus of FIG. 12 comprises a beam splitter40 and a pair of opposed mirrors or retro reflective prisms 42 disposedon opposite sides of the beam splitter 40.

In use, the beam splitter 40 reflects some of the ring of incident lightfrom the lens of the present invention to the reflecting member 42 onthe right in FIG. 2. The light from the right-hand reflecting member 42is reflected through the beam splitter 40, a number of times. At eachpass through the beam splitter 40 some of the light is reflected backtowards an eye of the observer. Further, the size of the reflected imagering diminishes with each pass so that reflected images that have beenreflected a large number of times are smaller than images which havebeen reflected a lesser number of times. The result is that the observersees a plurality of concentric rings 44 which are of circular shape.Further, some of the incident light will pass directly through the beamsplitter 40 and be reflected from a cornea 46 straight back through thebeam splitter 40 towards an eye of the observer. If the cornea 46 isastigmatic, the image 48 reflected from the cornea 46 will be ellipticalas discussed above. The plurality of circular rings 44 of different sizereflected from the reflecting members 42 enables a ready assessment ofthe degree of ellipticity of the image 48 to be made by the observer.

It is envisaged that the keratoscope of the present invention could besold as part of a package for an intraocular lens as a major applicationof the keratoscope of the present invention lies in the closure ofincisions made in the cornea after insertion of an intraocular lens inthe eye.

Typical packages for intraocular lens having keratoscopes in accordancewith the present invention, frangibly attached thereto are shown inFIGS. 13 and 14. Further, it is envisaged that the keratoscope lens ofthe present invention could be formed with a package for an intraocularlens such as those shown in FIGS. 13 and 14, so that the package itselfcould be used as a keratoscope.

Further, in an alternative form of packaging, the keratoscope could beincorporated in a sterile, flexible feature package which incorporates asmall chart with a number of images marked thereon. The images of thechart would be of varying degrees of ellipticity corresponding withdegrees of astigmatism ranging from, for example, 0 diopters to 8.00diopters as shown in FIG. 14a. Thus, this chart provides the observerwith a ready guide as to the degree of ellipticity of a keratoscopicimage reflected from a cornea and thus the degree of astigmatism of thecornea.

Further, when a surgeon has made an incision in an eye and has completedthe surgical procedure, it is necessary to close the incision by meansof sutures. It is important that the sutures be of the required degreeof tension to avoid inducing an undesirable degree of astigmatism in theeye.

In FIG. 15 there is shown a further embodiment of the present inventionwhich could be used during the suturing procedure to ensure that thesutures are at the appropriate degrees of tension so as to minimise theproblem of excessive astigmatism.

The apparatus of FIG. 15 comprises an opaque base plate 50 having aviewing aperture 52 formed therein. A handle 54 is attached to the baseplate 50. A rotatable transparent disc 56 is mounted to a pin 58 on theplate 50 such that the disc 56 is rotatable in a plane parallel to theplane of the plate 50. As shown, the disc 56 is formed with a pluralityof toroidal lens 60 of varying degrees of ellipticity as indicated bythe diopter number adjacent each lens 60. The disc 56 can be readilyrotated manually by the surgeon so as to bring each lens 60 to theviewing aperture 52 in turn. If the lens 60 of greatest ellipticity inthe viewing aperture 52 and an image thereof reflected from a cornea issubstantially circular, the cornea has a high degree of astigmatization.Alternatively, if the image reflected from the lens 60a which issubstantially circular, is also circular, then the cornea has little orno astigmatism. By rotating the disc 56, the surgeon can monitorcontinuously the degree of astigmatism of the cornea and adjust hissutures accordingly.

Still further, it is envisaged that the keratoscope of the presentinvention could be used in conjunction with a microscope containing areticule in the eye piece thereof. The reticule would typically comprisea number of concentric rings representative of differing degrees ofastigmatism. The keratoscopic image reflected from the cornea isobservable in the eye piece of the microscope in known manner and issuperimposed on the image from the reticule. Thus, the observer can forman assessment of the degree of ellipticity of the reflected image byobserving which ring of the reticule corresponds with the length of thelong axis of an ellipse of the reflected image. The reticule could beilluminated or non-illuminated. A binocular microscope incorporating areticule 70 is shown in FIG. 16.

Yet still further, it is envisaged that the apparatus of the presentinvention could be used in conjunction with a slit lamp. The slit lampsold under Trade Mark "Rodenstock" has a retractable diffuser and can beused in conjunction with the keratoscope of the present inventionwithout modification. However, other types such as that sold under theTrade Mark "Haag-Streit" may need to be provided with a diffusingelement such as a piece of frosted plastics material or glass or adiffusing lens to provide a beam large enough to illuminate the whole ofthe lens of the keratoscope of the present invention.

The keratoscope of the present invention can be formed from plasticsmaterial or glass and can be formed by moulding techniques or by cuttingtechniques. Further, a glass keratoscope can be formed by bending an endof a molten glass rod to a circular shape and joining the free end tothe rod.

Further, it is envisaged that a plastics material keratoscope inaccordance with the present invention could incorporate ingredientswhich make the keratoscope biodegradable or photodegradable.

Modifications and variations such as would be apparent to a skilledaddressee are deemed within the scope of the present invention.

What is claimed is:
 1. A keratoscope which comprises a lighttransmitting lens which is of annular shape, has a toroidal surface andis disposed in a plane, wherein said lens is attached to a handle whichextends away from said lens in a direction generally in alignment withthe plane of said lens, and said lens and said handle are formed in onepiece.
 2. A keratoscope according to claim 1, characterized bycomprising a plurality of the lenses of differing sizes.
 3. Akeratoscope according to claim 2, characterized in that the lenses aredisposed in a single plane.
 4. A keratoscope according to claim 2,characterized in that the lenses are disposed in different planes.
 5. Akeratoscope according claim 2, characterized in that the plurality oflenses are of varying degrees of ellipticity.
 6. A keratoscope accordingto claim 1, characterized in that the keratoscope comprises an opaquebase plate with a viewing aperture and a rotatable plate member to thebase plate, wherein the rotatable plate is provided with a plurality oflenses arranged to be brought in them to the viewing aperture uponrotation of the rotatable member and being of varying ellipticity.
 7. Alens useful as a keratoscope characterized in that the lens is of acircular or semi-circular shape and has a light transmitting lens ofannular shape with a toroidal surface which is attached to a handle, thelens and handle being formed in one piece, the keratoscope being furthercharacterized in that there is provided a beam splitter and a respectivesurface to provide a circular image for comparative purposes.